CHEMISTRY OP THE LEUCOMAINES. 323 



little urea, then decomposed With hydrogen sulphide, ami 

 the filtrate, rendered alkaline with ammonium hydrate, is 

 con<vntrat<-d to a small volume. On standing, pure hypo- 

 xanthine crystallizes out. The filtrate from the silver salt 

 of hypoxanthineon being rendered alkaline with ammonium 

 hydrat ^ivc- a precipitate which formerly was regarded as 

 consisting entirely ot' the xanthine silver compound, but 

 which from the investigations of SALOMON, lias, ^>een shown 

 to le a mixture of the salts of xanthine, paraxanthine, 

 ami heteroxanthine. 



The separation of thes.- bases is efl'eeted ly the solubility 

 of the free bases in ammoniuni hydrate. For this purpose 

 the precipitate of the mixed silver salts is decomposed with 

 hydrogen sulphide, and the filtrate, rendered anunoniacal to 

 remove traces of phosphates and oxalates, i- moderately 

 concentrated. After standing twenty-four hours, heteroxan- 

 thine crystallizes out, partly in finely formed sheaves and 

 tufts of needles, partly in radially striated masses. The 

 fluid is decanted from the crust of heteroxanthine which 

 forms in the bottom of the beaker, and after being concen- 

 trated somewhat is again allowed to stand. In tnis way a 

 second crop is obtained, and this is repeated till finally the 

 separated masses scarcely give a precipitate with sodium 

 hydrate. All the heteroxanthine is now united and dis- 

 solved in a little hot water by the aid of sodium hydrate. 

 After twenty-four hours the greater part of the heteroxan- 

 thine crystallizes out in bunches of crystals of sodium 

 heteroxanthine, while a small part together with any traces 

 of xanthine remains in solution. The crystalline ma-- i.- 

 dried by pressure, dissolved in a little water, and the solu- 

 tion neutralized by addition of hydrochloric acid, when the 

 heteroxanthin; 1 -.-paratc- as a pulverulent precipitate. To 

 remove any traces of paraxan thine, dissolve in hydrochloric 

 acid; on standing forty-eight hours the hetcroxanthine salt 

 separates, while the easily soluble salt of paraxanthine 

 remains in solution. To obtain the pure tree hetcroxau- 

 t.hine, the hydrochloric salt is evaporated with ammonium 

 hydrate; the well-washed residue of heteroxanthine is then 

 di--ilved in dilute ammonia, the solution filtered, evapor- 



